How to Offset Muscle Fatigue

Since the 1920s, scientists have associated the limits of endurance performance with the ability to transport and consume oxygen, most often focused on VO2 max. Despite how much attention is given to VO2 max collectively among physiologists, coaches and runners, it doesn't fully explain differences in performances between runners.

While you need a high VO2 max to be a good distance runner, running performance is influenced not only by factors related to oxygen consumption, but also by factors related to muscle fiber recruitment, force production and fatigue resistance. I have lab-tested many athletes who have an elite-level VO2 max, but few of them were capable of running at the elite or even sub-elite level because they didn't exhibit those other factors.

When your muscles exceed their aerobic metabolic capacity to re-synthesize energy (adenosine triphosphate or ATP) for muscle contraction, a number of problems begin to arise inside them that cause fatigue, most notably an increase in the concentration of hydrogen and potassium ions and the two products of ATP breakdown -- inorganic phosphate (Pi) and adenosine diphosphate (ADP). Each of these metabolites causes a specific problem inside muscles, including inhibiting the production of ATP from the metabolic pathway glycolysis, interfering with muscles' electrical charges, inhibiting calcium release (the trigger for muscle contraction) from its storage site in muscles, and inhibiting specific enzymes involved in muscle contraction. All of these factors lead to a decrease in muscle force production and your running speed. So, what can you do to delay muscle fatigue?

TEMPO RUNS AT LACTATE THRESHOLD PACE

While the lactate threshold is the fastest running speed above which lactate accumulates and acidosis occurs, what it really represents, in simple terms, is your ability to withstand fatigue and run hard for long periods of time. Research has shown that people with less fatigueable muscles produce less lactate during exercise, have a higher lactate threshold, and are able to perform at higher relative exercise intensities for prolonged periods.

For example, a study published in Journal of Sports Science and Medicine in 2008 found that cyclists who had greater quadriceps muscle fatigue resistance had a higher lactate threshold. However, the cyclists' fatigueability didn't relate to VO2 max, suggesting that the lactate threshold specifically reflects muscle performance and not cardiovascular performance. Another study published in Journal of Applied Physiology in 1993 found that, while VO2 max and running economy were similar between black and white South African runners, the black runners, who were better runners, were able to sustain a higher fraction of their VO2 max, had a lower blood lactate concentration when running at speeds above the lactate threshold, and exhibited greater fatigue resistance of the quadriceps muscles on a test of muscular endurance. While it's hard to conclude cause and effect, it's likely that the greater fatigue resistance and the ability to sustain a higher fraction of VO2 max are related to the lower blood lactate concentration (which reflects a lower anaerobic contribution and a better lactate removal capacity).

To improve your lactate threshold and thus your fatigue resistance, you need to increase the amount of time you spend running at your lactate threshold. Improving your lactate threshold pace allows you to run faster before you fatigue because it allows you to run faster before anaerobic metabolism begins to play a significant role. If you can improve your lactate threshold pace by 20 seconds per mile, that would correspond to a 1-minute improvement in a 5K since your 5K race pace will increase in concert with your lactate threshold pace.

5 to 10 miles at 10 to 15 seconds per mile slower than lactate threshold pace

2 sets of 4 x 1,000m at 5 to 10 seconds per mile faster than lactate threshold pace with 45 seconds rest between repeats and 2 minutes rest between sets

10 miles easy + 4 miles at lactate threshold pace

Lactate threshold pace, which should feel comfortably hard, is about 10 to 15 seconds per mile slower than 5K race pace (or about 10K race pace) for runners slower than about 40:00 for 10K (about 80 to 85 percent maximum heart rate). For highly trained and elite runners, the pace is about 25 to 30 seconds per mile slower than 5K race pace, about 15 to 20 seconds per mile slower than 10K race pace, often close to half marathon race pace (about 90 percent maximum heart rate).

SPRINTING AND PLYOMETRIC TRAINING

Research has shown that sprint training improves neuromuscular capacity to produce force and power, which can improve running economy and delay muscle fatigue. A study published in European Journal of Applied Physiology in 2006 found that the average speed attained during a 5K time trial was significantly correlated to the average speed attained during a 150m sprint.

The researchers also found a strong relationship between muscle activity at the 3K point of a 5K time trial and the average speed attained during the 5K, suggesting that runners who can maintain their level of muscle recruitment in the middle stages of a race (i. e., runners whose muscles fatigue less) perform better than runners whose level of muscle recruitment decreases. Thus, even for a distance runner, it's important to be fast and be able to maintain a high level of muscle fiber recruitment and muscle force production.

Plyometric training, which includes hopping, bounding, and jumping exercises involving repeated rapid eccentric (lengthening) and concentric (shortening) muscle contractions, increases muscles' rate of force development. Plyometrics take advantage of the characteristic that muscles produce more force during the concentric contraction if the contraction is immediately preceded by an eccentric contraction.

Therefore, to get the most out of plyometric training, you must concentrically contract your muscles immediately after eccentrically contracting them by spending as little time on the ground as possible between hops, bounds and jumps.

To increase muscle power and fatigue resistance, try these sprint and plyometric workouts:

4 to 6 x 150m at 400m race pace with 2 minutes rest between repeats

6 x 100m at close to top speed with 3 to 4 minutes rest between repeats

8 to 10 x 50m at close to top speed with 3 to 4 minutes rest between repeats

2 sets of 10 reps each of bleacher hops, squat jumps and box jumps with full recovery between sets

Train your muscles to resist fatigue and you'll have the fastest muscles of all your competitors, fast enough to challenge those with higher VO2 max values.

JASON R. KARP, PH. D., is a speaker, writer and exercise physiologist who coaches recreational runners to Olympic hopefuls through RunCoachJason.com and is director and coach of REVO2LT Running Team.